Secondary-emitter sensor position indicator

ABSTRACT

A secondary-emitter sensor position indicator has primary emitters that transmit light having primary wavelengths and at least one secondary emitter that transmits light having at least one secondary wavelength. A detector outputs a sensor signal in response to received light. An attachment assembly, in a sensor-on condition, positions the emitters and detector relative to a tissue site so that the sensor signal is substantially responsive to the primary wavelength light after attenuation by pulsatile blood flow within the tissue site and is negligibly responsive to the secondary wavelength light. The attachment assembly, in a sensor out-of-position condition, positions the secondary emitter relative to the tissue site so that the sensor signal is at least partially responsive to the secondary wavelength.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit under 35 U.S.C. §119(e)to U.S. Provisional Patent Application Ser. No. 61/104,890, filed Oct.13, 2008, titled Secondary-Emitter Sensor Position Indicator, herebyincorporated by reference herein.

BACKGROUND OF THE INVENTION

Pulse oximetry is a technique that utilizes a noninvasive sensor todetermine a person's oxygen status. An optical sensor used in pulseoximetry has light emitting diodes (LEDs) that transmit opticalradiation of red and infrared wavelengths into a tissue site. A detectorin the sensor responds to the intensity of the optical radiation afterattenuation by pulsatile arterial blood flowing within the tissue site.Based on this response, a processor determines measurements for SpO₂ andpulse rate among other parameters. Pulse oximeters capable of readingthrough motion induced noise are available from Masimo Corporation(“Masimo”) of Irvine, Calif. Moreover, portable and other pulseoximeters capable of reading through motion induced noise are disclosedin at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,157,850, 6,002,952,and 5,769,785, which are owned by Masimo and are incorporated byreference herein. Corresponding low noise optical sensors are alsoavailable from Masimo and are disclosed in at least U.S. Pat. Nos.6,985,764, 6,813,511, 6,792,300, 6,256,523, 6,088,607, 5,782,757,5,758,644 and 5,638,818. Such reading through motion pulse oximeters andlow noise sensors have gained rapid acceptance in a wide variety ofmedical applications, including surgical wards, intensive care andneonatal units, general wards, home care, physical training andvirtually all types of monitoring scenarios. Moreover, pulse oximeterscapable of reading through motion induced noise including Radical®,Rad-5™, Rad-8™, Rad-9™ and PPO+™ monitors and low noise optical sensorsincluding LNOP®, LNCS® and SofTouch™ disposable, reusable, reSposable™and multisite sensors and cables are also available from Masimo.

Further, noninvasive blood parameter monitors capable of measuringparameters in addition to SpO₂, such as HbCO, HbMet and Hbt andcorresponding multiple wavelength optical sensors are also availablefrom Masimo. Noninvasive blood parameter monitors and correspondingmultiple wavelength optical sensors are described in at least U.S.patent application Ser. No. 11/367,013, filed Mar. 1, 2006, titledMultiple Wavelength Sensor Emitters and U.S. patent application Ser. No.11/366,208, filed Mar. 1, 2006, titled Noninvasive Multi-ParameterPatient Monitor, both assigned to Masimo Laboratories, Irvine, Calif.(Masimo Labs) and both incorporated by reference herein. Moreover,multiple parameter monitors and multiple wavelength sensors includingRadical-7™, Rad57™ and Rad87™ monitors and Rainbow™-brand adhesive andreusable sensors are available from Masimo. MS- and MX-brand processorboards are also available from Masimo.

SUMMARY OF THE INVENTION

Problems arise if a pulse oximeter or other blood parameter monitor isconnected to an optical sensor that is not properly positioned on atissue site or becomes partially or completely dislodged from a patient,a sensor out-of-position condition including sensor-off and sensormis-position conditions. When an optical sensor is properly positionedon a tissue site, the detector only receives LED emitted light that haspropagated via the tissue site to the detector after tissue scatteringand absorption. Thus, the AC detector signal that results accuratelyreflects the differential absorption of constituents in the pulsatilearterial blood. If a sensor is off a tissue site or is mis-positioned onthe tissue site, the detector may directly receive LED emitted light,i.e. light that has not propagated through any tissue. Despite a sensorout-of-position condition, a blood parameter monitor may continue todetect an AC signal, which can be induced at the detector by other thanpulsatile arterial attenuation of LED emitted light. Small patientmovements, vibrations, air flow or other perturbations may cause thepathlength between the LEDs and detector to vary, resulting in an ACdetector signal that can be mistakenly interpreted by the monitor as dueto pulsatile arterial blood. Further, ambient light may reach thedetector, and any modulation of the ambient light due to AC power, powerfluctuations, moving objects, such as a fan, among other perturbationscan also be mistaken as a pulsatile arterial signal. Sensorout-of-position errors are serious because a blood parameter monitor maystill display a normal measurement, potentially leading to criticalmissed events, such as an oxygen desaturation.

An aspect of a sensor position indicator regards an optical sensor witha sensor-on condition in which the optical sensor is attached to andaligned with a tissue site so as to transmit light into the tissue siteand detect the light after attenuation by pulsatile blood flow withinthe tissue site and a sensor out-of-position condition in which thesensor is unattached to or misaligned with the tissue site. The sensorposition indicator comprises an optical sensor having primary emittersand a detector. The primary emitters generate light generally centeredaround each of multiple primary wavelengths. The primary emitterstransmit light into a tissue site in a sensor-on condition. Thedetector, in the sensor-on condition, outputs a sensor signal responsiveto the primary wavelength light after attenuation by pulsatile bloodflow within the tissue site. A secondary emitter generates lightgenerally centered around a secondary wavelength. The secondary emittertransmitted light is at least substantially attenuated by the tissuesite. The detector, in the sensor-on condition, is at leastsubstantially blocked by the tissue site from the secondary emitter sothat the sensor signal is not responsive to the secondary wavelengthlight. The detector, in a sensor out-of-position condition, is at leastpartially exposed to the secondary emitter so that the sensor signal isresponsive to the secondary wavelength light. A processor is responsiveto the sensor signal so as to calculate a blood-related physiologicalparameter in the sensor-on condition and so as to indicate the sensor isunattached to or misaligned with the tissue site in the sensorout-of-position condition.

In various embodiments, the optical sensor has a sensor mis-positionedcondition in which the optical sensor is misaligned with the tissuesite. The sensor position indicator further comprises a second secondaryemitter that generates light generally centered around the secondarywavelength. The detector, in the sensor mis-positioned condition, is atleast substantially blocked from the second secondary emitter by thetissue site and is at least partially exposed to the secondary emitterso that the sensor signal is not responsive to the second secondaryemitter and is responsive to the secondary emitter. The processor isresponsive to the sensor signal so as to indicate the optical sensor ismisaligned with the tissue site in the mis-positioned sensor condition.The optical sensor also has a sensor-off position in which the opticalsensor is unattached to or substantially misplaced on the tissue site.The detector, in the sensor-off condition, is at least partially exposedto the secondary emitter and the second secondary emitter so that thesensor signal is responsive to both the secondary emitter and the secondsecondary emitter. The processor is responsive to the sensor signal soas to indicate that the optical sensor is unattached to or substantiallymisplaced on the tissue site in the sensor-off condition.

The optical sensor also has a sensor over-positioned condition where thetissue site is over-inserted into the optical sensor. The sensorposition indicator further comprises a third secondary emitter thatgenerates light generally centered around the secondary wavelength. Thedetector, in the sensor-on condition, is at least substantially exposedto the third secondary emitter so that the sensor signal is responsiveto the third secondary emitter. The detector, in the sensorover-positioned condition, is at least substantially blocked from thethird secondary emitter by the tissue site so that the sensor signal isnot responsive to the third secondary emitter. The processor isresponsive to the sensor signal so as to indicate the tissue site isover-inserted into the optical sensor in the sensor over-positionedcondition. The primary wavelengths may include red and IR and thesecondary wavelength may be blue or green. The secondary emitter may belocated external to the optical sensor so that the secondary wavelengthlight is ambient light with respect to the optical sensor. The secondaryemitter may be driven asynchronously relative to the primary emitters.

An aspect of an optical sensing method comprises providing an opticalsensor having a primary emitter and a detector. The primary emitter isactivated with a primary drive signal so as to transmit light having aprimary wavelength into a fleshy tissue site. A secondary emitter isactivated with a secondary drive signal so as to transmit light having asecondary wavelength proximate the fleshy tissue site. The primarywavelength light is detected after attenuation by pulsatile blood flowwithin the tissue site. The secondary wavelength light is detected. Aphysiological parameter is calculated according to detected primarywavelength light. A sensor position of the primary emitter and thedetector relative to the fleshy tissue site is determined according tothe detection of secondary wavelength light.

In various embodiments, the primary drive signal and the secondary drivesignal are synchronized so that on periods of the secondary drive signaloccur during off periods of the primary drive signal. Determining sensorposition may comprise indicating a sensor-on condition according toundetected secondary wavelength light during an on period of thesecondary drive signal and indicating a sensor out-of-position conditionaccording to undetected secondary wavelength light during on periods ofthe secondary drive signal. A second secondary emitter may be activatedwith a second secondary drive signal and a sensor-off conditionindicated according to the undetected secondary wavelength light duringon periods of the secondary drive signal and second secondary drivesignal. A sensor mis-position condition may be indicated according todetected secondary wavelength light during on periods of the secondarydrive signal and according to undetected secondary wavelength lightduring on periods of the second secondary drive signal. A thirdsecondary emitter may be activated with a third secondary drive signaland a sensor over-position condition indicated according to detectedsecondary wavelength light during on periods of the third secondarydrive signal.

An aspect of a physiological measurement system comprises an opticalsensor having primary emitters, at least one secondary emitter, adetector and an attachment assembly. A physiological monitor is incommunications with the optical sensor. The primary emitters transmitlight having a primary wavelengths. At least one secondary emittertransmits light having at least one secondary wavelength. The detectoroutputs a sensor signal in response to received light. The attachmentassembly, in a sensor-on condition, positions the emitters and detectorrelative to a tissue site so that the sensor signal is substantiallyresponsive to the primary wavelength light after attenuation bypulsatile blood flow within the tissue site and is negligibly responsiveto the secondary wavelength light. The attachment assembly, in a sensorout-of-position condition, positions at least one secondary emitterrelative to the tissue site so that the sensor signal is at leastpartially responsive to the at least one secondary wavelength.

In various embodiments, a first secondary emitter is located in a firstposition relative to the primary emitters. A second secondary emitter islocated in a second position relative to the primary emitters. Theattachment assembly, in a sensor mis-positioned condition, positions thesecondary emitters relative to the tissue site so that the sensor signalis negligibly responsive to the first secondary emitter and at leastpartially responsive to the second secondary emitter. The attachmentassembly, in a sensor-off condition, may position the secondary emittersrelative to the tissue site so that the sensor signal is at leastpartially responsive to the first secondary emitter and the secondsecondary emitter. A third secondary emitter may be located in a thirdposition relative to the primary emitters. The attachment assembly, in asensor-on condition, positions the secondary emitters relative to thetissue site so that the sensor signal is negligibly responsive to thefirst and second secondary emitters and at least partially responsive tothe third secondary emitter. The attachment assembly, in a sensorover-positioned condition, positions the secondary emitters relative tothe tissue site so that the sensor signal is negligibly responsive tothe first, second and third secondary emitters. A processor portion ofthe physiological monitor may operate on the sensor signal so as todetermine the position of a finger relative to the sensor according toat least multiple ones of a sensor-on condition, a sensorout-of-position condition, a sensor off condition and a sensormis-positioned condition. A display portion of the physiological monitormay be responsive to the processor determination of sensor and fingerposition so as to graphically depict the position of a finger relativeto the sensor. An alarm portion of the physiological monitor may beresponsive to the processor determination of sensor and finger positionso as to audibly indicate the position of a finger relative to thesensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective illustration of a physiological measurementsystem utilizing a sensor position indicator;

FIG. 2 is a block diagram of a physiological measurement systemutilizing a sensor position indicator;

FIGS. 3A-B are general block diagrams of a secondary-emitter sensorposition indicator illustrating sensor-on and sensor-off conditions,respectively;

FIGS. 4A-B are side view illustrations of a secondary-emitter sensorposition indicator illustrating sensor-on and sensor-off conditions,respectively;

FIGS. 5A-C are timing diagrams for a secondary-emitter sensor positionindicator illustrating a primary-emitter drive signal and correspondingdetector output signals for a sensor-off condition with synchronous andasynchronous secondary emitters, respectively;

FIGS. 6A-C are side view illustrations of a secondary-emitter sensorposition indicator illustrating sensor-on, sensor mis-positioned andsensor-off conditions, respectively;

FIGS. 7A-D are timing diagrams for a secondary-emitter sensor positionindicator illustrating primary and secondary emitter drive signals andcorresponding detector output signals for sensor-on, sensormis-positioned and sensor-off conditions;

FIGS. 8A-D are side view illustrations of a secondary-emitter sensorposition indicator illustrating sensor-on, sensor over-positioned,sensor mis-positioned and sensor-off conditions, respectively; and

FIGS. 9A-E are timing diagrams for a secondary-emitter sensor positionindicator illustrating primary and secondary emitter drive signals andcorresponding detector output signals for sensor-on, sensorover-positioned, sensor mis-positioned and sensor-off conditions,respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-2 illustrate a physiological measurement system 100 whichmeasures blood constituents and related parameters, such as oxygensaturation, pulse rate, perfusion index (PI), pleth variability index(PVI™), HbCO, HbMet and Hbt, to name a few. The physiologicalmeasurement system 100 includes an optical sensor 110 applied to atissue site 10, a monitor 130 and a cable 150 that physically andelectrically connects the sensor 110 to the monitor 130. Advantageously,the physiological measurement system 100 also utilizes a sensor positionindicator responsive to improper placement of the sensor 110 on a fingeror other tissue site 10, as described in detail below.

As shown in FIGS. 1-2, the patient monitor 130 communicates with thesensor 110 to receive one or more intensity signals indicative of one ormore physiological parameters. Drivers 134 convert digital controlsignals into analog drive signals 154 capable of driving primaryemitters 112 that transmit optical radiation having multiple primarywavelengths. The drivers 134 also provide drive signals 156 capable ofdriving secondary emitters 116 having one or more secondary wavelengths.A detector 114 responds to the intensity of the optical radiation afterattenuation by pulsatile blood flow within the tissue site 10 andgenerates a corresponding sensor signal 152. A front-end 132 convertsthe analog sensor signal 152 into digital data input to a digital signalprocessor (DSP) 138. The DSP 138 comprises any of a wide variety of dataand signal processors capable of executing programs for determiningphysiological parameters from input data. The instrument manager 140 maycomprise one or more microcontrollers providing system management, suchas monitoring the activity of the DSP 138. The instrument manager 140also has communications 142 with displays, alarms and user input/output(I/O) 144. In an embodiment, a display 144 depicts the position of afinger relative to the sensor according to any of a sensor on, a sensorout-of-position, a sensor off and a sensor mis-positioned condition.

Also shown in FIGS. 1-2, in an embodiment a sensor position indicatorincorporates external secondary emitters 170 located outside of thesensor 110. In an embodiment, a sensor position indicator incorporatesinternal secondary emitters 116 located inside the sensor 110. Thesecondary emitters 116, 170 have one or more wavelengths selected to beat least substantially attenuated by tissue. In an embodiment, secondaryemitter wavelengths are selected from the blue or green region of thevisible spectrum so as to be highly absorbed by water and, hence,substantially attenuated by the substantial water content of tissue. Inthis manner, the sensor signal 152 responsive to a secondary emitter116, 170 is indicative of a sensor-off or a sensor mis-positionedcondition. That is, for the detector 114 to sense a secondary emitter116, 170, the detector 114 must be at least partially uncovered by thetissue site 10.

As shown in FIG. 1, external secondary emitters 170 can be placed in oneor more locations in or around the measurement system 100. Thesesecondary emitters 170 enable the detection of a sensor-off or sensormis-positioned condition via generation of ambient light having at leastone secondary wavelength. As examples, external secondary emitters 170can be disposed on the monitor 130, on the cable connector 160, in thesurrounding room, such as on a wall 180, or on other instruments in theroom (not shown), or combinations of these locations. External secondaryemitters 170 may be free running, driven by the monitor in sync withprimary emitters or may be driven by another instrument.

As shown in FIG. 2, one or more internal secondary emitters 116 areplaced in a sensor proximate a primary emitter 112 and distal a detector114 used for blood parameter measurements. These secondary emitters 116enable the detection of a sensor-off or sensor mis-positioned conditionvia generation of sensor generated light having at least one secondarywavelength. Internal secondary emitters 116 may be free running ordriven by the monitor in sync with the primary emitters.

FIGS. 3A-B illustrate a sensor 200 having a secondary emitter configuredfor sensor position indication. The sensor 200 has primary emitters 210capable of transmitting light having primary wavelengths (λp) 212 into atissue site 10. A detector 240 is capable of detecting the transmittedlight 212 after attenuation by the tissue site 10 and outputting aprimary signal 250 responsive to the detected light 214. The primarysignal 250 is indicative of at least one physiological parametercorresponding to the tissue site 10. Advantageously, the sensor 200 isassociated with at least one secondary emitter 220 having at least onesecondary wavelength (λs) 213 that is at least substantially attenuatedby the tissue site 10. In this manner, the response of the detectorsignal 250 to the secondary emitter 220 is indicative of sensorposition, as described in further detail below.

As shown in FIG. 3A, a sensor-on condition 201 is where the tissue site10 is properly placed relative to the detector 240 so that accuratephysiological measurements can be made. In particular, a primary emitter210 is placed so as to illuminate a blood-perfused tissue site 10, suchas a nail bed, and the detector 240 is positioned so that only lighttransmitted by the primary emitter 210 and attenuated by pulsatile bloodflowing within the tissue site 10 is received by the detector 240.Specifically, in a sensor-on condition 201, the detector 240 is notexposed to ambient light or light transmitted directly from emitter 210to detector 240 without tissue site attenuation, such as by light-pipingor reflection around the tissue site or otherwise. For example, in asensor-on condition 201, constraints on the placement and relativelocation of emitter, tissue site and detector result in a sensor signalhaving a negligible contribution from light having a secondarywavelength λs 213.

As shown in FIG. 3B, a mis-positioned sensor condition or a sensor-offcondition 202 is where the tissue site 10 is displaced relative to thedetector 240 so that light having a secondary wavelength λs 213 reachesthe detector 240, i.e. the detector signal 250 is also responsive to asecondary emitter 220. For example, in a mis-positioned sensor conditionor a sensor-off condition 202, a sensor signal could have a substantialcontribution from ambient light or other transmitted light that has notreach the detector 240 via tissue site 10 attenuation. Variousembodiments of a sensor position indicator utilizing a secondary emitterare described with respect to FIGS. 4-9, below.

FIGS. 4A-B illustrate a secondary emitter sensor embodiment in asensor-on condition and a mis-positioned sensor condition, respectively.The sensor 400 has a primary emitter 410 that emits light havingmultiple primary wavelengths λp into a tissue site 10 and a detector 420that detects the emitted light after attenuation by the tissue site 10.

As shown in FIG. 4A, in a sensor-on condition 405, the tissue site 10completely covers the detector 420. As such, light having a secondarywavelength λs is at least substantially attenuated by the tissue site 10so that the detector 420 is not responsive to a secondary emitter. Thatis, the failure to detect emission from one or more secondary emittersindicates a sensor-on condition 405.

As shown in FIG. 4B, in a mis-positioned sensor condition 406, thedetector 420 is exposed to light having a secondary wavelength λsincluding light from one or more secondary emitters. That is, thedetection of wavelength λs from one or more secondary emitters indicateseither a mis-positioned sensor condition 406 or a sensor-off condition(not shown).

As shown in FIGS. 4A-B, one or more external secondary emitters 170(FIG. 1) or internal secondary emitters 116 (FIG. 2) have at least onesecondary wavelength λs that is at least substantially attenuated by thetissue site 10. Accordingly, a sensor position relative to the tissuesite 10 is indicated according to whether a secondary wavelength isdetected. In an embodiment, internal secondary emitters, if any, aredriven synchronously with the primary emitters, as described withrespect to FIGS. 5A-B, below. In an embodiment, external secondaryemitters, if any, are free-running, i.e. driven asynchronously from theprimary emitters, as described with respect to FIG. 5C, below. In anembodiment, a detector response in one or more time slots where noprimary emitters are activated indicates a sensor-off condition, asdescribed with respect to FIGS. 5A-C, below. In an embodiment, theemitter 410 is an array of LEDs including LEDs that emit primarywavelengths and LEDs that emit one or more secondary wavelengths. Anemitter array is described in U.S. patent application Ser. No.11/367,013, cited above and incorporated by reference herein.

FIGS. 5A-C illustrate time diagrams for an emitter drive signal 500 andcorresponding detector signals 520, 540 with synchronous andasynchronous secondary emitters, respectively. These emitter drive 500and detector signals 520, 540 correspond to a sensor utilizing aninternal or external secondary emitter, such as described with respectto FIGS. 4A-C, above. As shown in FIG. 5A, during primary emitter enableperiods 501-503, drive current is supplied from monitor drivers 134(FIG. 2) to selected primary emitters in sequence, causing the selectedemitters to turn on and emit optical energy at a particular wavelength.During OFF periods 511-513, no drive current is supplied to any emitter,allowing demodulation of the detector signal. Detector signaldemodulation is described in U.S. Pat. No. 5,919,134 entitled “Methodand Apparatus for Demodulating Signals in a Pulse Oximetry System,”which is assigned to Masimo Corporation, Irvine, Calif. and incorporatedby reference herein.

Also shown in FIG. 5A, the drive signal 500 represents emitter drivecurrents activated and deactivated to various emitters. Included areemitter currents 501-503 for activating primary emitters 112 (FIG. 2)that transmit light having multiple wavelengths λ_(p1), λ_(p2), . . .λ_(pn) into a tissue site 10 (FIG. 2). Also included are emittercurrents 506 for synchronously activating one or more secondary emittershaving one or more wavelengths during an inactive period 510 for theprimary emitters. For example, a single internal secondary emitter 116(FIG. 2) of wavelength λ_(s) may be activated after the primary emitters112 (FIG. 2) have each be activated in sequence and before the start ofanother primary activation sequence, as shown. In another embodiment,there are no synchronous emitter currents 506 for activating secondaryemitters. Rather, secondary emitters, either internal or external arefree-running or are otherwise activated asynchronously from the primarydrive currents, as described with respect to FIG. 5C, below.

As shown in FIG. 5B, a detector signal 520 represent detector current152 (FIG. 2) in response to the emitter transmitted light afterabsorption by pulsatile bloodflow within the tissue 10 (FIG. 2). Inparticular, the detector signal 520 has response periods 521-523corresponding to the primary emitter enable periods 501-503 (FIG. 5A)and off periods 531-533 corresponding to the primary emitter off periods511-513 (FIG. 5A). Advantageously the detector signal 520 may also haveone or more secondary emitter response intervals 530 that indicate asensor-off condition. The DSP 138 (FIG. 2), for example, processes asecondary emitter response interval 530 so as to detect a synchronoussecondary emitter response 526, which indicates a sensor-off condition.Correspondingly, failure to detect a synchronous secondary emitterresponse 526 within the interval 530 when a secondary emitter isactivated 506 (FIG. 5A) is indicative of a sensor-on condition.

As shown in FIG. 5C, a detector signal 540 also represents detectorcurrent 152 (FIG. 2) in response to the emitter transmitted light afterabsorption by pulsatile blood flow within the tissue 10 (FIG. 2),including response periods 541-543 corresponding to the primary emitterenable periods 501-503 (FIG. 5A) and off periods 551-553 correspondingto the primary emitter off periods 511-513 (FIG. 5A). Advantageously thedetector signal 540 may also have one or more secondary emitter responseintervals 550 used to detect an asynchronous secondary emitter response546 indicative of a sensor-off condition. That is, the DSP 138 (FIG. 2),may process an interval 550 known to be outside of any primary emitteractivation sequence so as to determine if there is a detector responseto an asynchronous secondary emitter, such as a free-running externalemitter. Detection of a known secondary emitter activation sequencewithin the interval 550 is indicative of a sensor-off condition, andfailure to detect such a sequence may be indicative of a sensor-oncondition. As described above, the secondary emitter response intervals530, 550 may include one or more on/off cycles of one or moresynchronously or asynchronously activated secondary emitters.

FIGS. 6A-C illustrate a multiple secondary-emitter sensor 600advantageously configured to indicate multiple improper sensor placementconditions. In particular, the multiple secondary-emitter sensor 600 hasa sensor-on condition 605, a sensor mis-positioned condition 606 and asensor-off condition 607. The sensor 600 has a primary emitter 610 thatemits light having multiple primary wavelengths λ_(p) into a tissue site10 and a detector 620 that detects the emitted light after attenuationby the tissue site 10. In the embodiment shown, the sensor 600 has twosecondary emitters 630, 640 that emit light having a secondarywavelength λs and that are placed relative to the primary emitter 610 soas to indicate the two improper placement sensor conditions.

As shown in FIG. 6A, in the sensor-on condition 605, tissue completelycovers the detector 620 so that the detector 620 is not responsive tosecondary emitters 630-640 of wavelength λ_(s). As shown in FIG. 6B, inthe sensor mis-positioned condition 606, the detector 620 is exposed toat least one secondary emitter 630 and is blocked by tissue from atleast one secondary emitter 640. As shown in FIG. 6C, in the sensor-offcondition 607, the detector 620 is exposed to light transmitted frommultiple secondary emitters 630-640. Advantageously, a sensormis-positioned condition 606 is differentially indicated from asensor-off position 607 so that an attached monitor can more accuratelyinform a healthcare professional or monitor operator of an appropriatecorrective action.

Although a multiple secondary-emitter sensor 600 is described above withtwo secondary emitters 630, 640 placed proximate to and on either sideof the primary emitter 610, in other embodiments there may be more thantwo secondary-emitters. In other embodiments, the secondary emitters mayboth be located on the same side of the primary emitter, the secondaryemitters may be placed at various locations around the primary emitter,the secondary emitters may be co-located within the primary emitterpackage or the secondary emitters may be placed at various combinationsof the above-described sensor locations. Further, some or all of thesecondary emitters may have the same or similar wavelengths λ_(s) orsome or all of the secondary emitters may have distinct wavelengths λs₁,λs₂, . . . λs_(n).

FIGS. 7A-D illustrate sensor timing diagrams corresponding to a sensorhaving multiple secondary emitters, such as described with respect toFIGS. 6A-C, above. As shown in FIG. 7A, emitter drive signals 700include activated and deactivated drive currents to multiple primaryemitters 701-703 and multiple secondary emitters 705-706. In particular,during a secondary emitter activation interval 710, secondary emitters630, 640 (FIGS. 6A-C) are activated 705, 706 in sequence withintervening OFF periods.

As shown in FIGS. 7B-D, a detector signal 720 corresponding to theemitter drive signals 700 is generated by the detector 114 (FIG. 2) andtransmitted to the monitor 130 (FIG. 2) as a detector current 152 (FIG.2). As shown in FIG. 7B, in a sensor-on condition 605 (FIG. 6A), lighttransmitted from the secondary emitters 630, 640 (FIG. 6A) is at leastsubstantially absorbed by tissue 10 (FIG. 6A) properly placed betweenthe emitters and the detector 620 (FIG. 6A). Hence, there is no detectorcurrent corresponding to secondary emitter activation during theactivation interval 730 (FIG. 7B). Thus, the monitor 130 (FIGS. 1-2) candetermine that there is proper placement of the sensor 110 (FIGS. 1-2).

As shown in FIG. 7C, in a mis-positioned sensor condition 606 (FIG. 6B),light transmission from at least one secondary emitter 630 (FIG. 6B) isnot at least substantially absorbed by tissue, because the tissue site10 (FIG. 6B) is not properly placed between the emitters 630, 640 (FIG.6B) and the detector 620 (FIG. 6B). Hence, there is detector current 725corresponding to a secondary emitter drive current 705 (FIG. 7A) duringthe activation interval 730. Thus, the monitor 130 (FIGS. 1-2) candetermine that the sensor 110 (FIGS. 1-2) is mis-positioned.

As shown in FIG. 7D, in a sensor-off condition 607 (FIG. 6C), lighttransmission from all secondary emitters 630, 640 (FIG. 6C) is not atleast substantially absorbed by tissue, as the sensor is substantiallymisplaced on the tissue site or is completely off of the tissue site 10(FIG. 6C). Hence, there is detector current 725-726 corresponding toeach secondary emitter drive current 705, 706 (FIG. 7A) during theactivation interval 730. Thus, the monitor 130 (FIGS. 1-2) can determinethat the sensor 110 (FIGS. 1-2) is substantially or completely off ofthe tissue site.

FIGS. 8A-D illustrate a secondary emitter/detector sensor 800 havingsecondary emitters and a secondary detector advantageously configured toindicate a sensor on condition and multiple improper sensor conditions.In particular, the secondary emitter/detector sensor 800 has a sensor-oncondition 805, an over-positioned sensor condition 806, a sensormis-positioned condition 807, and a sensor-off condition 808. In anover-positioned sensor condition 806, the sensor 800 indicates that thetissue site is inserted too far into the sensor. An over-positionedsensor condition 806 may occur, for example, in a removable finger clipsensor where a fingertip is over inserted, such as when a finger nail orother finger structure bypasses a blocking structure or indent.

The secondary emitter/detector sensor 800 has a primary emitter 810 thatemits light having multiple primary wavelengths λp into a tissue site 10and a primary detector 820 that detects the emitted light afterattenuation by the tissue site 10. In the embodiment shown, the sensor800 also has three secondary emitters 830-840 that emit light having asecondary wavelength λs, which are placed relative to the primaryemitter 810 so as to indicate the three improper placement sensorconditions.

As shown in FIG. 8A, in the sensor-on condition 805, tissue completelycovers the detector 820 so that the primary detector 820 is notresponsive to secondary emitters 830-840. The secondary detector 825,however, is responsive to a secondary emitter 835 placed distal theprimary emitter 810.

As shown in FIG. 8B, in the sensor over-positioned condition 806, thesecondary detector 825 is not responsive to the secondary emitter 835.That is, light transmission from the secondary emitter 835 is at leastsubstantially absorbed when tissue is over inserted between a secondaryemitter 835 and secondary detector 825.

As shown in FIG. 8C, in the sensor mis-positioned condition 807, thedetector 820 is exposed to at least one secondary emitter 830 and isblocked by tissue from at least one secondary emitter 840. As shown inFIG. 8D, in the sensor-off condition 808, the detector 620 is exposed tolight transmitted from multiple secondary emitters 630-640.Advantageously, the various improperly placed sensor conditions 806-808are differentially indicated from each other so that an attached monitorcan more accurately inform a healthcare professional or monitor operatorof an appropriate corrective action.

FIGS. 9A-E illustrate sensor timing diagrams corresponding to asecondary emitter/detector sensor 800 (FIGS. 8A-D), such as describedabove. These timing diagrams including input emitter drive signals 900and corresponding combined primary and secondary detector output signals950-980 indicating a sensor-on condition and various improper sensorposition conditions. As shown in FIG. 9A, emitter drive signals 900include drive currents activated and deactivated to multiple primaryemitters 901-903 and multiple secondary emitters 905-907 during asecondary emitter activation interval 910.

As shown in FIG. 9B, in a sensor-on condition 805 (FIG. 8A), a primarydetector response current 921-923 is generated by the primary detector820 (FIG. 8A) in response to light received during emitter activation901-903. Also, a secondary detector response current 927 is generated bythe secondary detector 825 (FIG. 8A) in response to light receivedduring a secondary response interval 930 in response to secondaryemitter activation 907.

As shown in FIG. 9C, in a sensor over-positioned condition 806 (FIG.8A), a primary detector response current 921-923 is generated by theprimary detector 820 (FIG. 8A) as described with respect to FIG. 9B,above. However, the secondary detector response current 927 for a sensorover-position condition is substantially null during the secondaryactivation interval 930 as light transmission at wavelength λs is atleast substantially absorbed by the tissue over-inserted between thedetector and the secondary emitter 825, 835 (FIG. 8B).

As shown in FIG. 9D, in a mis-positioned sensor condition 807 (FIG. 8C)light transmission from at least one secondary emitter 830 (FIG. 8C) isnot at least substantially absorbed by tissue, which is not properlyplaced between the secondary emitters 830, 840 (FIG. 8C) and the primarydetector 820 (FIG. 8C). Hence, there is primary detector current 925corresponding to a secondary emitter drive current 905 (FIG. 9A) duringthe activation interval 930. Thus, the monitor 130 (FIGS. 1-2) candetermine that the sensor is mis-positioned.

As shown in FIG. 9E, in a sensor off condition 808 (FIG. 8D) lighttransmission from all secondary emitters 830 is not at leastsubstantially absorbed by tissue, which is either substantiallymisplaced between the secondary emitters 830, 840 (FIG. 8D) and theprimary detector 820 (FIG. 8D) or the sensor is entirely off of thetissue site. Hence, there is detector current 925-927 corresponding tosecondary emitter drive current 905-907 (FIG. 9A) during the activationinterval 930. Note that primary detector current 921-923 in response toprimary emitter drive current 901-903 may have an AC component thatappears normal, i.e. due to pulsatile blood absorption, despite theabsence of tissue, as described in the summary, above.

A secondary-emitter sensor position indicator has been disclosed indetail in connection with various embodiments. These embodiments aredisclosed by way of examples only and are not to limit the scope of theclaims that follow. One of ordinary skill in art will appreciate manyvariations and modifications.

1. A sensor position indicator having an optical sensor with a sensor-oncondition in which the optical sensor is attached to and aligned with atissue site so as to transmit light into the tissue site and detect thelight after attenuation by pulsatile blood flow within the tissue siteand a sensor out-of-position condition in which the sensor is unattachedto or misaligned with the tissue site, the sensor position indicatorcomprising: an optical sensor having a plurality of primary emitters anda detector; the primary emitters generating light generally centeredaround each of a plurality of primary wavelengths; the primary emitterstransmitting light into a tissue site in a sensor-on condition; thedetector, in the sensor-on condition, outputting a sensor signalresponsive to the primary wavelength light after attenuation bypulsatile blood flow within the tissue site; a secondary emitter thatgenerates light generally centered around a secondary wavelength; thesecondary emitter transmitted light is at least substantially attenuatedby the tissue site; the detector, in the sensor-on condition, is atleast substantially blocked by the tissue site from the secondaryemitter so that the sensor signal is not responsive to the secondarywavelength light; the detector, in a sensor out-of-position condition,is at least partially exposed to the secondary emitter so that thesensor signal is responsive to the secondary wavelength light; and aprocessor responsive to the sensor signal so as to calculate ablood-related physiological parameter in the sensor-on condition and soas to indicate the sensor is unattached to or misaligned with the tissuesite in the sensor out-of-position condition; wherein the secondaryemitter is driven asynchronously relative to the primary emitters. 2.The sensor position indicator according to claim 1 wherein the opticalsensor has a sensor mis-positioned condition in which the optical sensoris misaligned with the tissue site, the sensor position indicatorfurther comprising: a second secondary emitter that generates lightgenerally centered around the secondary wavelength; the detector, in thesensor mis-positioned condition, is at least substantially blocked fromthe second secondary emitter by the tissue site and is at leastpartially exposed to the secondary emitter so that the sensor signal isnot responsive to the second secondary emitter and is responsive to thesecondary emitter, and the processor is responsive to the sensor signalso as to indicate the optical sensor is misaligned with the tissue sitein the mis-positioned sensor condition.
 3. The sensor position indicatoraccording to claim 2 wherein the optical sensor has a sensor-offposition in which the optical sensor is unattached to or substantiallymisplaced on the tissue site: the detector, in the sensor-off condition,is at least partially exposed to the secondary emitter and the secondsecondary emitter so that the sensor signal is responsive to both thesecondary emitter and the second secondary emitter, and the processor isresponsive to the sensor signal so as to indicate that the opticalsensor is unattached to or substantially misplaced on the tissue site inthe sensor-off condition.
 4. The sensor position indicator according toclaim 3 wherein the optical sensor has a sensor over-positionedcondition where the tissue site is over-inserted into the opticalsensor, the sensor position indicator further comprising: a thirdsecondary emitter that generates light generally centered around thesecondary wavelength; the detector, in the sensor-on condition, is atleast substantially exposed to the third secondary emitter so that thesensor signal is responsive to the third secondary emitter; thedetector, in the sensor over-positioned condition, is at leastsubstantially blocked from the third secondary emitter by the tissuesite so that the sensor signal is not responsive to the third secondaryemitter; the processor is responsive to the sensor signal so as toindicate the tissue site is over-inserted into the optical sensor in thesensor over-positioned condition.
 5. The sensor position indicatoraccording to claim 4 wherein the primary wavelengths include red and IRand the secondary wavelength is at least one of blue and green.
 6. Asensor position indicator having an optical sensor with a sensor-oncondition in which the optical sensor is attached to and aligned with atissue site so as to transmit light into the tissue site and detect thelight after attenuation by pulsatile blood flow within the tissue siteand a sensor out-of-position condition in which the sensor is unattachedto or misaligned with the tissue site, the sensor position indicatorcomprising: an optical sensor having a plurality of primary emitters anda detector; the primary emitters generating light generally centeredaround each of a plurality of primary wavelengths; the primary emitterstransmitting light into a tissue site in a sensor-on condition; thedetector, in the sensor-on condition, outputting a sensor signalresponsive to the primary wavelength light after attenuation bypulsatile blood flow within the tissue site; a secondary emitter thatgenerates light generally centered around a secondary wavelength; thesecondary emitter transmitted light is at least substantially attenuatedby the tissue site; the detector, in the sensor-on condition, is atleast substantially blocked by the tissue site from the secondaryemitter so that the sensor signal is not responsive to the secondarywavelength light; the detector, in a sensor out-of-position condition,is at least partially exposed to the secondary emitter so that thesensor signal is responsive to the secondary wavelength light; and aprocessor responsive to the sensor signal so as to calculate ablood-related physiological parameter in the sensor-on condition and soas to indicate the sensor is unattached to or misaligned with the tissuesite in the sensor out-of-position condition; wherein the secondaryemitter is located external to the optical sensor so that the secondarywavelength light is ambient light with respect to the optical sensor. 7.An optical sensing method comprising: providing an optical sensor havinga primary emitter and a detector; activating the primary emitter with aprimary drive signal so as to transmit light having a primary wavelengthinto a fleshy tissue site; activating a secondary emitter with asecondary drive signal so as to transmit light having a secondarywavelength proximate the fleshy tissue site; detecting the primarywavelength light after attenuation by pulsatile blood flow within thetissue site; detecting the secondary wavelength light; calculating aphysiological parameter according to detected primary wavelength light;determining a sensor position of the primary emitter and the detectorrelative to the fleshy tissue site according to the detection ofsecondary wavelength light; and synchronizing the primary drive signaland the secondary drive signal so that on periods of the secondary drivesignal occur during off periods of the primary drive signal.
 8. Theoptical sensing method according to claim 7 wherein the determiningcomprises: indicating a sensor-on condition according to undetectedsecondary wavelength light during an on period of the secondary drivesignal; and indicating a sensor out-of-position condition according toundetected secondary wavelength light during on periods of the secondarydrive signal.
 9. The optical sensing method according to claim 8 furthercomprising: activating a second secondary emitter with a secondsecondary drive signal; and indicating a sensor-off condition accordingto the undetected secondary wavelength light during on periods of thesecondary drive signal and second secondary drive signal.
 10. Theoptical sensing method according to claim 9 further comprising:indicating a sensor mis-position condition according to detectedsecondary wavelength light during on periods of the secondary drivesignal and according to undetected secondary wavelength light during onperiods of the second secondary drive signal.
 11. The optical sensingmethod according to claim 10 further comprising: activating a thirdsecondary emitter with a third secondary drive signal; and indicating asensor over-position condition according to detected secondarywavelength light during on periods of the third secondary drive signal.12. A physiological measurement system comprising: an optical sensorhaving a plurality of primary emitters, at least one secondary emitter,a detector and an attachment assembly; a physiological monitor incommunications with the optical sensor; the primary emitters transmitlight having a plurality of primary wavelengths; the at least onesecondary emitter transmits light having at least one secondarywavelength; the detector outputs a sensor signal in response to receivedlight; the attachment assembly, in a sensor-on condition, positions theemitters and detector relative to a tissue site so that the sensorsignal is substantially responsive to the primary wavelength light afterattenuation by pulsatile blood flow within the tissue site and isnegligibly responsive to the secondary wavelength light, and theattachment assembly, in a sensor out-of-position condition, positionsthe at least one secondary emitter relative to the tissue site so thatthe sensor signal is at least partially responsive to the at least onesecondary wavelength; wherein the secondary emitter is drivenasynchronously relative to the primary emitters.
 13. The physiologicalmeasurement system according to claim 12 further comprising: a firstsecondary emitter located in a first position relative to the primaryemitters; a second secondary emitter located in a second positionrelative to the primary emitters; and the attachment assembly, in asensor mis-positioned condition, positions the secondary emittersrelative to the tissue site so that the sensor signal is negligiblyresponsive to the first secondary emitter and at least partiallyresponsive to the second secondary emitter.
 14. The physiologicalmeasurement system according to claim 13 wherein the attachmentassembly, in a sensor-off condition, positions the secondary emittersrelative to the tissue site so that the sensor signal is at leastpartially responsive to the first secondary emitter and the secondsecondary emitter.
 15. The physiological measurement system according toclaim 14 further comprising: a third secondary emitter located in athird position relative to the primary emitters; the attachmentassembly, in a sensor-on condition, positions the secondary emittersrelative to the tissue site so that the sensor signal is negligiblyresponsive to the first and second secondary emitters and at leastpartially responsive to the third secondary emitter; and the attachmentassembly, in a sensor over-positioned condition, positions the secondaryemitters relative to the tissue site so that the sensor signal isnegligibly responsive to the first, second and third secondary emitters.16. The physiological measurement system according to claim 15 furthercomprising: a processor portion of the physiological monitor; and theprocessor operating on the sensor signal so as to determine the positionof a finger relative to the sensor according to at least multiple onesof a sensor-on condition, a sensor out-of-position condition, a sensoroff condition and a sensor mis-positioned condition.
 17. Thephysiological measurement system according to claim 16 furthercomprising: a display portion of the physiological monitor; and thedisplay responsive to the processor determination of sensor and fingerposition so as to graphically depict the position of a finger relativeto the sensor.
 18. The physiological measurement system according toclaim 17 further comprising: an alarm portion of the physiologicalmonitor; and the alarm responsive to the processor determination ofsensor and finger position so as to audibly indicate the position of afinger relative to the sensor.